Using a heater with a thermostat controlled by an Apex gives you some redundancy. In my 65g I run an Aquael Gold 300 (300W) as my main heater, controlled by my Apex. It’s thermostat is set to turn off just above the Apex off temperature. That way if my Apex goes nuts and won’t shut it off, the heater’s thermostat will.
I then run a cheaper Aqua One 200W backup heater that is not controlled by my Apex, set using it’s thermostat to turn on just below the Apex off temperature. That way if my main heater fails, or my Apex fails to turn it on, the backup kicks in. As this heater is generally not used I don’t have an issue with a cheaper unit.
I also keep an Eheim Jaeger 150 as a spare. Eheim heaters are over-rated, meaning the 150W Eheim is equivalent to most other 200W+ heaters.
Sorry if the brands above (apart from the Eheim) aren’t the same in the US market as I am Australia based.